There are many situations in industry or transportation that require the use of multiple energy storage systems. Typically, a long term energy storage system, such as a battery or fuel cell, may be used to supply the bulk of the energy required to operate equipment or power electronics. Often times there is a need for quick bursts of energy and power that cannot always be supplied by such long term energy systems without causing damage to the system that results in a shortened operating life of such systems, or even the risk of overheating and explosion. In these cases it is desirable to add an additional energy storage system to supply shorter, but higher power, bursts of energy to the equipment. Getting these two energy sources to work together, however, is challenging. Therefore it is highly desirable to provide a system and method that addresses the challenges of having the two energy systems work together.
Hybrid vehicles typically use a conventional hydrocarbon combustion engine (e.g., using gasoline, diesel, compressed natural gas, ethanol, or a combination thereof) and an electric motor coupled to a battery. The battery provides power to the electric motor and in some cases stores power recovered from regenerative braking. In current hybrids, the battery usually has sufficient storage to assist the gasoline engine, but not to operate the vehicle using electric power only at freeway speeds. Plug-in Hybrid vehicles (PHEVs) are hybrid vehicles that have a higher electrical power/energy capacity, such that they can operate on electric power alone for short (e.g., less than 40 miles) trips. Plug-in hybrids typically recharge from an mains electric power supply (such as 110 Volts or 220 Volts at home or a higher voltage at a dedicated charging station).
Unfortunately, current problems with conventional current storage systems have limited the wider adoption of emerging PHEVs. For example, these conventional electrical power sources (e.g., batteries) are costly and have a limited life. Existing PHEV systems also do not last long, as rapid charging and discharging degrades the power source over time.
Power and current demands of such a vehicle vary significantly. For example, when a vehicle is at a stoplight, the vehicle is in a stopped steady state and requires very little power or current. When a vehicle is cruising on a freeway, the vehicle may be in a cruising steady state and may also require lower current or power. Accelerating, climbing a hill, or towing a load, however, required significantly more current or power, and may required a continuous heavy power draw. For example. typical freeway cruising may require only 30% of the power required for accelerating onto a freeway or for passing. Maintaining steady freeway speed on a grade (e.g., in a climb mode) may require as much power as acceleration in highway operation.
If rechargeable batteries are subjected to high current draw above certain limits (often specified by the battery manufacturer) the battery performance and useful life of the battery will be degraded.
Therefore, it would be desirable to have an energy storage system that addresses the above problems, by allowing for high current/power demands without degrading the performance or useful life of the power source.